The invention relates to a method of producing leadthroughs on hollow profiles, the hollow profile being acted upon by a high fluidic pressure in an internal high-pressure forming tool, and a dome-like secondary shaped element being formed outwards in the radial direction from this hollow profile by the fluid pressurizing, whereupon the secondary shaped element is reverse drawn into the interior of the hollow profile by means of a punch at the prevailing internal high pressure, whereupon, to open the leadthrough, a punched slug is cut out of the base of the reverse-drawn secondary shaped element by means of the punch. The invention also relates to a device for carrying out this method.
A method or a device of the generic type has been disclosed by German Patent Document DE 195 30 055 A1 (corresponding U.S. Pat. No. 5,799,524). To form bearing bosses on transverse links or double-transverse-link front axles of motor vehicles, a reverse-drawing process operated with fluidic internal high pressure is described here. In this case, dome-like necking is formed out of a hollow body under internal high pressure, this dome-like necking being reverse drawn by a punch in a central region into the interior of the hollow profile against the internal high pressure. The reverse drawing is effected until the necking wall acted upon by the punch comes to bear against the opposite wall of the hollow profile. Up to that point, the opposite wall is supported in a fixed position by a counterstay punch. Once the walls come to bear against one another, the counterstay punch is retracted. The punch which hitherto served for the reverse drawing is advanced further, in the course of which, by means of a cutting edge, it cuts off that part of the necking wall which is acted upon. The wall supported by the counterstay punch is sheared off via a sharp edge of the leadthrough in which the counterstay punch is guided. In a further forward movement, the reverse-drawing punch presses the bent-in margin of the necking cutout outwards and at the same time presses it against the opening margin of the cutout opening of the hollow-profile wall opposite the necking. This type of reverse drawing is not possible in some applications, since the hollow-profile material cannot apply the requisite expansions during the forming on account of its material properties and/or the geometrical dimensions of the leadthrough to be produced (excessive height), as a result of which cracks or fractures may therefore occur in the process, so that the process reliability in the method of producing such leadthroughs or bearing bosses is not ensured. Furthermore, due to the generous reverse drawing, the thickness of the hollow-profile material is greatly reduced in the transition region from the leadthrough to the surrounding component, as a result of which the strength of the leadthrough is adversely affected, this strength being absolutely necessary in some practical applications for attaching further components, for example, shock absorbers, or for making a bearing bush in the leadthrough.
An object of the invention is to develop a method of the generic type and a device of the generic type to the effect that the process reliability when producing the leadthrough is ensured even in the case of a hollow-profile material having low formability and the strength of the hollow profile in the transition region to the leadthrough is retained.
According to the invention, this object is achieved with regard to the production method by providing a method of the above noted type, wherein in each case a secondary shaped element is formed out of the hollow profile at two opposite locations, wherein the respective secondary shaped elements each are reverse drawn after the forming, into the hollow profile interior by a punch in such a way that their bases come to bear inside the hollow profile in the final state of the reverse drawing, and wherein the punched slug is severed from the respective base by one punch serving as a plunging punch plunging into the other punch.
According to the invention this object is also achieved by providing a device for producing leadthroughs on hollow profiles, comprising an internal high-pressure forming tool which has a branch branching off radially from a tool impression for forming a dome-like secondary shaped element by fluidic pressurizing, and a punch which is guided in the branch of the impression and by means of which the secondary shaped element can be reverse drawn into the interior of the hollow profile at the prevailing internal high pressure, and, after the reverse drawing, a punched slug can be severed from the base of the reverse-drawn secondary shaped element, wherein two branches are formed in the forming tool and are arranged on two opposite sides of the impression, wherein in each case a punch for the reverse drawing of in each case one secondary shaped element is guided in the two branches, wherein the punches are controlled in such a way that, after the end position during the reverse-drawing operation has been reached, the bases of the secondary shaped elements bear against one another inside the hollow profile, wherein one of the punches comprises a sleeve, the inside diameter of which sleeve is larger than the outside diameter of the opposite punch in alignment with the clear width of the sleeve, and furthermore contains a support which is guided inside the sleeve and on which the base of the associated secondary shaped element can be supported, and wherein the punch, for severing punched slugs from the bases of the secondary shaped elements, can be moved into the sleeve, whereas the support is controlled in such a way that it gives way outwards when the punch plunges into the sleeve.
Thanks to the invention, due to the smaller drawing length, now required, of the secondary shaped element or of the necking and smaller reverse-drawing travel, the transition region to the leadthrough is subjected to considerably less loading by a reduction in thickness of the material, so that the strength of the hollow profile there is sufficiently ensured. Furthermore, the use of materials which have only low extension properties and low elastic limits and therefore had to be ruled out in the case of the known methods is thus possible for the hollow profile. Since the risk of cracks in the hollow profile no longer occurs on account of the reduced tensile stress, the process reliability is ensured. By the separation of the punched slug in the punch receiving the plunging punch, the punched slug, in a simple manner, can either be removed via the punch from the impression of the internal high-pressure forming tool or pushed back into the cutout opening of the secondary shaped elements and removed upon removal of the component, so that the problem occurring in other methods with the removal of the punched slug from the impression can easily be rectified and the process reliability for subsequent forming operations is ensured due to the fact that there are no overlooked punched slugs in the impression or there are no punched slugs in the impression which are jammed at locations of the impression where access is difficult. On account of the active mechanical punching by interaction between two punches, very small hole diameters can also be produced, in contrast to punching operated solely by internal high pressure.
Expedient configurations of the invention may be gathered from the description and the claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.